Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$71.57	9.619%	$78.4543	$78.45	$78.45	$78.50
Purchase #2	$40.43	12.200%	$45.3625	$45.36	$45.35	$45.40
Purchase #3	$65.39	8.750%	$71.1116	$71.11	$71.10	$71.10
Purchase #4	$160.32	13.834%	$182.4987	$182.50	$182.50	$182.50
Purchase #5	$39.99	5.790%	$42.3054	$42.31	$42.30	$42.30
Purchase #6	$197.27	13.531%	$223.9626	$223.96	$223.95	$224.00
Purchase #7	$242.66	7.411%	$260.6435	$260.64	$260.65	$260.60
7 purchase totals =	$817.63		$904.3386	$904.33	$904.30	$904.40